Fuel burner control system



May 13, 1941. w MCGRATH 2,242,183

- FUEL BURNER CONTROL SYSTEM Filed June 21, 1939 LIMIT CONTROL bl Hi0 V inventor William I1. M Grall'L.

Patented May 13, 1941 FUEL momma comm srs'mu William L. McGrath, St. Paul, Minn, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application June 21, 1939, Serial No. 280,302

. 16 Claims.

This invention relates to a simplified system for electrically controlling fuel burners and is directed more particularly to'that type of system wherein the fuel feeding device is directly controlled by timers, making it possible to obtain the proper control without the necessity for relays and complicated circuits.

One of the main objects of the invention is to provide a system in which a timer closes a switch in the circuit to the fuel feeding device and then reopensthe switch after a predetermined length of time if combustion has not been obtained.

Another object is to provide a combustion responsive device for preventing the timer from reopening the switch if combustion takes" place thereby maintaining the circuit to the fuel feeding device closed as long as the timer remains energized.

Still another object is to provide a system in which the timers are thermal elements having electric heaters, one of the elements being energized to close the switch in the circuit to the fuel feeding device and the other being energized in response to combustion to physically prevent the reopening of the switch by the first timer.

Another object is to fix two birnetal timers at one end and connect them at their free ends, the timers being oppositely disposed so that when both are heated no motion will take place but when only one is heated that one will develope sufficient force to bend both of them.

Still another object is to pivotally mount a mercury switch and actuate it by means of a lever so mounted that as the lever rotates in one direction the mercury switch will be first'closed and then opened.

These and other objects will readily become apparent to those skilled in the art as the fol-.

lowing specification is read in the light of the accompanying drawing in which:

Figure 1 is a diagrammatic representation of one form of my invention, the parts being shown in their deenergized positions; I

Figure 2 is a partial view showing the two timers, the combustion responsive switch, and the switch in control of the fuel feeding device in the positions they occupy shortly after th first timer has been energized; I

Figure 3 is a view similar to Figure 2 showing the position of the parts after combustion has been obtained; v

Figure 4 is a view similar to Figures 2 and 3 showing thev position of the parts in the absence of combustion and when the switch has been locked in open position, and

Figure 5 shows a modified form of my invention.

Referring now to Figure 1, the main control for my fuel burner control system may be in the form of a room thermostat indicated generally I at H which is shown as comprising a bimetal coil l2 which is fixed at one end and which carries at its free end a switch blade 13. On a decrease in temperature to a predetermined value, the bimetal coil l2 will move the switch blade 13 into engagement with the stationary. contact H.

. by means of a stop ll.

The room thermostat II is wired in series with the usual limit control l5 which may act to open the circuit on an increase in boiler temperature or pressure above a predetermined value.

Fastened to the bracket [1 is one end of a bimetallic timer I8. The timer i8 is provided with an electric heating element ill for producing a timed movement thereof. Carried on the upper end of the timer I8 is an actuating block 20 which is provided with a depression 2| in which is seated a rounded end 22 of a lever 23 which is shown as pivoted at 24. The other end of the lever 23 is provided with a roller 25 which engages the under side of a second lever 26 which is shown to be pivoted at 21. Lever 26 carries thereon a mercury switch generally indicated at 30. This switch may be of the usual glass tube type which contains a globule of mercury 3| which acts to bridge and unbridge the electrodes 32 and 33.

Secured to the bracket 35 is a second bimetallic timer 36 with which is associated an electrical heater 31. A latch member 33 is carried on the free end of the bimetallic timer 36. The latch 38 is adapted to cooperate with the camsurface 39 and depression 40 on the actuating block 23 under certain circumstances which are described in detail hereinafter. On being heated by the heater 31, the bimetallic timer 3S warps in a downwardly direction and its motion is limited Reset member 42 comprises a knob 43 and stem 44 which is slidably received in an opening in a stationary member '45. A coil spring 46 biases the reset member to the position shown in Figure 1. If the bimetallic timer 36 is in its deflected position, it may be manually moved by pressing on the knob ll of the reset member. This action becomes necessary in releasing the latch as will be explained more fully hereinafter.

A combustion responsive device is indicated generally at it and comprises a switch arm 43 emf Manners we and stationary contact 59. This device is shown diagrammatically but it will be appreciated that the switch arm 49 is actuated by means of an element which is responsive to combustion in the furnace controlled by the present system. As is 5 well known in the art, the element is connected to the switch arm by means of a slip friction device sothat the switch is actuated not in response'to any definite temperature but rather in response to a change in temperature produced by the appearance or disappearance-of a flame in the furnace. This switch is so arranged that when combustion is obtained the switch arm 49 will engage the stationary contact 55.

/ This system is provided with the usual fuel feeding device in the form of an electric burner motor 5|. An ignition means '52 is also provided for igniting the fuel delivered by the motor 5|. Electric power is supplied to the system from supply lines 53 and 54 over a double-polesinglethrow manually operated switch indicated at 55.

In considering the operation of this system, let it be assumed that the room thermostat ll has been satisfied for a sufficient length of time to permit the combustion device 48 to have separated the switch arm 49 from the contact 50 and for the bimetallic timers i8 and to have returned to their cold positions. Under these conditions the burner motor 5| will be deenergized and the temperature in the room will de- 30 crease. After the room temperature has decreased to a predetermined value, the bimetallic element l2 will move the switch arm |3 into engagement with the stationary, contact l4 which will establish the following circuit: supply line 5 53, manual switch 55, conductors 51, 58, and 59, bimetallic element l2 switch arm l3, contact |4, conductorv 50, limit. control l5, conductor 5|, electric heater l9, conductors 52, 53, and 54, and manual switch 55 back to the other supply line 54. Theabove circuit energizes the heater l9 and causes the bimetallic-timer 18 to heat up and flex to the left. This causes a rotation of the lever.23 toward a vertical position resulting I in a raising of the lever 25 which causes the mercury 3| to bridge electrodes 32 and 33. Figure 2 shows the parts in this position. When the mercury bridges the electrodes 32 and 33 it closes the following circuit: from conductor 59 to conductor 55, electrode 33, mercury 3|, electrode 32, conductors 35 and 51, burner motor 5|, and conductors 53 and 69 back to the conductor 53. This circuit energizes the burner motor 5| and it will be noted that the ignition means 52 is connected in parallel with motor 5| by means of conductors 15 and 1|. In other words, this system is a constant ignition system-wherein the ignition means is energized during the entire time that the burner motor is running. This system could easily be changed into an intermittent ig nition system by putting a switch in conductor 1 15 which can be opened by the combustion responsive device 49, or if desired, this switch could be opened by the timer 35 as it warps downwardly and strikes stop 4|.

Energization of the burner motor and ignition means will normally produce combustion within the furnace which will cause the combustion responsive device 45 tomove the switch arm 49 into engagement with the stationary contact 55.

This results in closing a circuit from the conductor 51 to conductor 13, switch arm 49, contact 59, conductor 14, electric heater 31, andconductor 15 back to conductor 54. Energization of the heater 31 will cause. the bimetallic timer 35 to heat up and warp in a downwardly direction. The timers l5 and 35 are so related that under normal conditions the timer I5 will close the mercury switch 39 to produce combustion resulting in the warping of the timer 35 which will heat up and engage the stop 4| before the timer II will have warped suillciently for the actuating block 25 to engage the latch 35.- With the bimetallic timer 35 in its hot position, the latch 35 acts as a stop for the actuating block 20 thereby preventing further warping of the timer l3 as is clearly shown in Figure 3. The arrangement is such that the timer l3 will be stopped in a position where it holds the mercury switch 35 closed and therefore the burner motor and ignition means will remain energized. This is the normal-running condition of the system.

As a result of the operation of the burner motor and ignition means, the temperature in the room will begin to rise and after it has reached a predetermined value the bimetallic element |2 will move the switch arm l3 out of engagement with the stationary contact l4. This results in breaking the circuit to the electric heater i9 and the bimetallic element l3 will begin to cool and return to its original position thereby opening the mercury switch 35. This breaks the circuit to the fuel burner motor and as a result the delivery of fuel to the burner will be stopped, In response to-the failure of combustion the combustion responsive device 48 will cause the switch arm 49 to separate from contact 50 and the iresultant deenergization of the electric heater 31 will cause the bimetallic timer 35 to return toits original position as shown in Figure 1.

If the bimetallic timer it closes the mercury switch 35 in response to a demand for heat by the room thermostat H and combustion does not take place, the heater 31 will remain deenergized' because the combustion responsive device 45 will not close the switch arm 49 against the contact 55. Thebimetallictimer l9 will thereforecontinue to flex toward the left as viewed in Figure l and the latch 35 will ride up on the cam surface 35 until it drops into the depression 43 in the actuator block 29. Atthis time the bimetallic timer II will have flexed far enough to rotate the lever 23 to a position where the lever 25 has reopened the mercury switch 30. This condition is illustrated in Figure 4 and at this time it will be seen that the latch 35 looks the bimetallic timer l3 in its warped position and prevents the reclosing of the mercury switch 35.

With the switch 50 locked in open position, the owner will be' aware of the fact that there isl something wrong with the system and he will open the manual switch 55 to remove the power from the system and remedy the cause of the trouble. He will then press the knob 43 of th reset member which will manually raise the bimetallic timer 35 permitting the bimetallic timer i3 to return to its cold position. After the reset member has been released, the manual switch 55l may be reclosed and the system is then in condition to make another attempt at a normal start.

It will be clear also that if the system is running normally with the parts in the position shown in Figure 3 and a combustion failure should occur, the combustion responsive device 45 will cause the switch arm 43 to separate from the contact 53. This will deenergize the heater 31 and the bimetallic timer 33 will warp upwardly until it releases, the actuatingblock 2 for movement by the bimetallic timer II. the heater l3 4: stili energized the bimetalli timer I will immediately swing the actuating block 20 to the left and cause the latch to lock the parts as shown in Figure 4. This will reopen the mercury switch 00 and the system will be shut down as described above.

If a power failure should occur at any time. both of the heaters I9 and 01 will be deenergized and the timers will return to their cold positions ,where they can make a normal start when power is resumed.

Figure 5 discloses a slightly modified form of my invention. This system is also provided with a room thermostat disclosed generally at 00 and provided with a bimetallic element 0| and switch arm 02 which cooperates with a stationary contact-00. The bracket 00 carries one end of each of a pair of bimetallic timers 06 and 06. The

a timer 00 carries a block 01 at its free end and timer 00 carries a block 00 at its free end. These two blocks are pivotally connected by means of the link 09. An electric heater 90 is positioned to heat the timer 05 and electric heater 9| is adapted to heat the timer 06. The block 00 is provided with a depression 92 in which is seated the rounded end 90 of the lever 90 shown as being pivoted at 95. The upper end of the lever 90 carries a mercury switch generally indicated at 00. This switch may be of the usual glass tube type and is shown as curved and having a pair of electrodes 91 and 90. A globule of mercury 99 is located within the tube to alternately bridge and unbridge the two electrodes. The le er' 90 is provided with a shoulder I00 with which a latch generally indicated at I0] is adapted to cooperate when the lever is rotated beyond a predetermined position in a counter-clockwise direction. The latch IOI comprises a stem I 02 which slides within a stationary support I03.

. Figure 5 by means of a light spring I05.

it is desired to reset the switch 96.

away from the stationary contact I09 in response has been at or above the desired value for some time, the parts will be in the posifion shown in Figure 5. At this time the mercury switch 96 will be in open position and the burner motor H0 and ignition device III will be deenergized. As a result the temperature will decrease in the room until the bimetallic element 0I causes the switch arm 02 to engage the stationary contact 03. This will establish the following circuit: line wire H2, conductor II5, bimetallic element 0|, switch arm 02, stationary contact 03, conductor II6, heater 9I, and conductor II1 back to line wire I I9. This circuit results in the energization of electric heater 9I which will heat the bimetallic timer 06 and cause it towarp toward the right. It will be noted at this time that the electric heating element 90 is shunted by the following circuit: line wire II2, conductors I2I, I22, switch arm I00, contact I09, conductor I23, protective resistance H9, and conductor I20 back to line with the contact 03.

wire I I 0. (Electric heater 00 is therefore deenergized.

As the bimetallic timer 00 heats up it will warp toward the right bending the bimetallic timer 00 in the same direction. This will came the lever 00 to rotate in a direction to cause the mercury. V 99 to bridge the electrodes 01 and 00.

This results in the energization of the burner motor H0 and ignition means III by means of the following circuit: from line wire II2, conductor I20, electrode 01, mercury 09, electrode 00, conductors I21 and I20, burner motor H0, and conductors I20 and I00 back to line wire H0. The ignition means is connected in parallel with the burner motor I I0 by means of conductors III and I02.

Energization of the burner motor I I0 and ignition means II I will normally produce combustion with the result that the combustion responsive device I01 will cause the switch arm I00 to separate from contact I09 and break the shunt circuit around the electric heater 00. The heater will now be energized by the following circuit: line wire U2, conductors HI and I00, electric heater 00, conductors I00 and III, protective resistance H9, and conductor I20 back to line wire I I0. The resultant energlzation of the heater 90 causes the bimetallic timer 00 to heat up and tend to warp toward the left in opposition to the warping movement of the bimetallic timer 06. The timers 05 and 00 are so related that at this time the timer 00 will exert just suflicient force on the timer 00 to hold it in a position to maintain the mercury switch 90 in closed position thereby maintaining the burner motor H0 and ignition means I energized. This is the normal running condition of the system.

When the room thermostat 00 is satisfied, the switch arm .02 will be moved out of engagement This will deenergize the heater 9I and cause the bimetallic timer 00 to flex toward the left and move the mercury switch 96 to open position. The burner motor H0 and ignition means III will then be deenergized and the resultant failure of combustion will cause the combustion responsive device I01 to move the switch arm I00 into engagement with contact I09 and reestablish the shunt circuit around the heater 90.

If the room thermostat calls for heat and energizes the heater 9|, the bimetallic timer 06 will close the mercury switch 96 energizing the burner motor H0 and ignition means III. If combustion is not established at this time, the switch arm I00 will remain in contact with the stationary contact I09 thus preventing the energizetion of the electric heater 90. The bimetallic timer 05 will therefore not oppose the warping of the bimetallic timer 06 toward the right and this movement continues until the mercury switch 96 is reopened thereby deenergizing the burner motor I I0 and ignition means III. At this time the latch I02 will be pulled beneath the shoulder I00 on the lever 90' by means of the spring I05, thereby locking the switch 96 in open position.

This apprises the owner of the fact that there is something wrong with the system and he opem;v

the manual switch in the power supply, such as the switch 55 shown in Figure 1, and corrects the trouble. After this he releases the latch IOI by means of the knob I00 and the parts return to the cold position. The system is now in a condition to make another attempt at a normal start when the manual power delivery switch is closed.

It will also be understood that if a flame failure occurs while the system is running normally the combustion responsive device ill! will move the switch arm I08 into engagement with contact ills which completes the shunt circuit around heater 90. The resultant deenergization of this heater permits the bimetallic timer 85 to be moved toward the right under the influence of the bimetallic timer 86 and its heater 91 and the mercury switch 96" will be reopened and latched in open positionas in the case when combustion is not obtained on starting.

On a failure of power the heaters 90 and 9| will be deenergized and the parts will return to their cold position where they will be ready to attempt a normal start.

This system may also be made an intermittent ignition system by having the combustion responsive device I01 open an ignition switch in conductor i3i or I32 as the combustion responsive device heats up.

It is thus seen that I have provided in the above described systems a simplified control in which no magnetic relays or complicated circuits are necessary and yet one which provides the.

proper safety featuresin the event of ignition failure or flame failure.

As various changes and modifications in these systems may occur to those who are skilled in the tion, first andsecond timers, a fuel feeding device, a first means for causing actuation of said first timer to render said fuel feeding device op erative, and second means responsive to .combustion produced by said fuel feeding device for causing actuation of said second timer, said first timer rendering said fuel feeding device inoperative again after a predetermined length of time unless said second means shall have caused actuation of said second timer first to cause it to mechanically oppose furthenmovement of said first timer to prevent such action.

2. A control system comprising in combination, first and second timers, a fuel feeding device, a first means for energizing said first timer to render said fuel feeding device operative, second means responsive to combustion produced by said fuel feeding device for energiizng said second timer, said first timer rendering said fuel feeding device inoperative again after a predetermined length of time unless said s ond means shall'have energized said second t mer first to cause it to mechanically oppose further movement of said first timer to prevent such action, and means for locking said first timer to prevent its automatic return in the event that it renders said fuel feeding device inoperative before said second timer is energized.

3. A control system comprising in combination, first and second timers, a fuel feeding device, a first means for energizing said first timer to render said fuel feeding device operative, second means responsive to combustion produced by said fuel feeding device-forenergizing said sec ond timer, said first timer rendering said fuel feeding device inoperative again after a predetermined length of time unless said second means shall have energized said second timer first to cause it mechanically opposefurther movement of saidfirst timer to prevent such action, means for locking said first timer to prevent its automatic return in the event that it renders said-fuel feeding device inoperaive before-said second timer is energized, and manual means for releasing said locking means to permit said first timer to return automatically to its original position.

4. A control system comprising in combination a first bimetallic element fixed at one end, a second bimetallic element fixed at one end, means connecting the free ends of said elements, a fuel feeding device, a switch in control thereof, a

10 heater for said first element, means for energizing said heater to cause said first element to warp and close said switch and then reopen it a predetermined time later, a second heater for said second element, and means responsive to combustion produced bysaid fuel feeding device for energizing said second .heater to cause said second element to resist the warping movement of said first element and thereby prevent said first element from reopening said switch. 5. A control system comprising in combination a first bimetallic element fixed at one end, a

, second bimetallic element fixed at one end, means connecting the free ends of said elements, a fuel feeding device, a switch in control thereof, a heater for said first element, means for energizin said heater to cause said first element to warp and close said switch and then reopen it a predetermined time later, a second h said second element, means responsive combustion produced by said fuel feeding device for energizing said second heater to cause said second element to resist the warping movement of said first element and thereby prevent said first element from reopening said switch, and means ,to lock said switch in open position after it has been reopened due to failure to obtain combustion. 6. A' fuel burner control-system comprising, a timer, an electrical fuel feeding device, a switch in control of said device, means for energizing said timer continuously to close said switch for a predetermined period of time and then open it again, means physically opposing said timer as a result of the establishment of combustion, for 43 preventing said timer from opening said switch,

and means for locking said switch in open position in the event that combustion does not occur before said timer reopens said switch. 7. A fuel burner control system comprising, a timer, an electrical fuel feeding device, a switch in control of said device, means for energizing said timer continuously to close said switch for. a predetermined period of time and then open it again, and means responsive to combustion for 53 physically opposing further movement 'of said timer thereby preventing it from reopening said switch.

8. A fuel burner control system comprising, a timer, an electrical fuel feeding device, a switch in control of said device, means for energizing said timer to close said switch for a predetermined period of time and then open it, thermally responsive means, a heater therefor, and means responsive to combustion for energizing said heater whereby said thermally means physically opposes said timer to prevent it from reopening said switch. i

9. A fuel burner control system comprising, a timer, an electrical fuel feeding device, a switch in control of said device, means for energizing said ;timer to close said switch for a predetermined period of time and then open it, thermally responsive means, a heater therefor, means responsive to combustion for energizing said heater whereby said thermally responsive means physically op,-

whereby said thermally responsive means physi-' cally opposes said timer to prevent it from re opening said switch, a latch carried by said thermally responsive means, said timer operativelyengaging said latch whereby said switch is locked in open position in the event that combustion does not take place, and means for manually moving said thermally responsive means to release said latch and permit said timer to return to its original position.

11. A fuel burner control system comprising, a timer, an electrical fuel feeding device, a switch in control of said device, means for energizing said timer to close said switch for a predetermined period of time and then open it, thermally responsive means, a heater therefor, means responsive to combustion for energizing said heater whereby said thermally responsive means physically opposes said timer to prevent it from reopening said switch, and means for latching said switch in open position in the event that combustion does not take place.

12. A control system comprising in combination, an electrical fuel feeding device, a control switch therefor, a bimetal timer associated with said switch, electric heating means for said timer, a main switch for energizing said heating means to cause said timer to first close said control switch and then open it again after a predetermined time, a second bimetal timer, an electric heating means therefor, and means responsive to combustion for energizing said last named heating means to cause said second timer to warp and prevent said first timer from reopening said switch.

13. A control system comprising in combination, an electrical fuel feeding device, a control switch therefor, a bimetal timer associated with said switch, electric heating means for said timer, a main switch for energizing said heating means to cause said timer to first close said control switch and then open it again after a predetermined time,

a second bimetal timer, an electric heating means therefor, means responsive to combustion for energizing said last named heat ng means to cause said second timer to warp and prevent said first timer from reopening said switch, and latch means, said latch means acting on failure to obtain combustion to lock said switch in open position.

14. A control system of the class described comprising in combination, an electrical fuel feeding device, an electric circuit therefor, a pivoted mercury switch in control of said circuit, a pivoted lever for tipping said mercury switch, a timer operatively associated with said lever, means for energizing said timer to rotate said lever and tip said mercury switch to closed position and then after a predetermined time to open position again, a resilient member carrying a latch, said latch cooperating with said timer after it has reopened said switch to lock said switch in open position,

said resilient member comprising a bimetallic eiement, a heater for said bimetallic element, and means responsive to combustion for energizing said heater to cause said element to warp and prevent said timer from reopening said switch.

15. A fuel burner control system comprising, a timer, an electrical fuel feeding device, a switch in control of said device, means for continuously energizing said timer to cause it to move in a direction to close said switch for a predetermined period of time and then open it again, and means responsive to combustion for physically preventing' said timer from moving sufliciently to open said switch, a subsequent failure of combustion rendering said last mentioned means incapable of preventing said timer from continuing its movement to open said switch. I

16. A control system comprising in combination, first and second timers which move to one position when energized and return to their original position when deenergized, an electrical fuel feeding device, means responsive to a demand for fuel for energizing said first timer and maintainingit energized so long as said demand exists, said timer upon energization first rendering said fuel feeding device operative and, after a predetermined period of time, rendering it inoperative again as said timer moves into its energized position, and means responsive to the combustion of the fuel for energizing said second timer and causing it to prevent the first timer from moving into its energized position if it has not already done so.

WILLIAM L. McGRATH. 

